The steering of optical beams has assumed increased importance as the use of such beams for communications and weaponry has proliferated. Conventional methods of steering optical beams include movable reflectors or refractors and electro-mechanical steering of arrays of deflectors, each of which steers a portion of the beam in parallel with the other deflectors in the array. Such beam steering techniques have become more important as various applications involving requirements for high phase coherence and accuracy of pointing have emerged. In particular, the propagation of collimated beams of light such as laser light over long distances require that such a collimated beam be of a relatively large diameter, retain phase coherence, provide for very low scattering of light in the deflection process, and be aimed with very high accuracy. These requirements are difficult to obtain with prior art techniques when high angular deflection rates are required of the beam steering apparatus. Those techniques are particulary inadequate when large diameter beams exceeding approximately 20 cm in diameter must be steered.
The use of conventional mechanical techniques requires that such beam steering devices have a low moment of inertia and impose minimum distortion while being rapidly pointed. In the past, approaches to accomplishing optical beam steering have included relatively large single reflectors and arrays of smaller reflectors or refractors. However, there are serious problems with these approaches. Phased arrays with many moving parts are complex and expensive to construct, are limited in the angular excursion they can accommodate and are relatively difficult to calibrate and synchronize with one another. Large reflectors may be constructed with large diameters and highly accurate surfaces to retain phase coherence and thus provide a collimated beam. However, such reflectors have relatively high moments of inertia and therefore, large drive power requirements when rapid beam steering is required. Any attempt to reduce the weight and inertia of such a system is likely to result in distortion being induced when the accelerations associated with rapid angular beam movement occur. Some approaches using liquid crystal arrays have been proposed for spatial intensity to position mapping, but such systems have been primarily related to phase conjugation and other intensity modification applications. The use of conventional electro-optic scanners is similarly restricted, since large diameter crystals are not available. Furthermore, very high voltages are required to generate the phase shifts with such scanners and the available scan angles are restricted.
From the above, it is clear that modern systems employing lasers for communications and weapons have created an as yet unfulfilled need for agile beam deflectors that retain spatial phase coherence and surface accuracy over large apertures and are capable of propagating light beams over great distances with minimal scattering and energy loss due to phase interference.